has_many doc inconsistency/missing info in upgrade doc related to dependent option behavior change from Rails 3 to 4

Gary_Weaver · December 16, 2013, 2:57pm

A team member just found the following out about an inconsistency in the Rails documentation. Although:

indicates for the dependent option: “When no option is given, the behaviour is to do nothing with the associated records when destroying a record.”

Which is consistent with the behavior, but in:

github.com

rails/rails/blob/4b4aeabb3605bd0cbd7dde10c1d2ac990c65379a/activerecord/lib/active_record/associations.rb#L988


      
          # +has_many+ and +has_and_belongs_to_many+ associations have the methods <tt>destroy</tt>,
          # <tt>delete</tt>, <tt>destroy_all</tt> and <tt>delete_all</tt>.
          #
          # For +has_and_belongs_to_many+, <tt>delete</tt> and <tt>destroy</tt> are the same: they
          # cause the records in the join table to be removed.
          #
          # For +has_many+, <tt>destroy</tt> and <tt>destroy_all</tt> will always call the <tt>destroy</tt> method of the
          # record(s) being removed so that callbacks are run. However <tt>delete</tt> and <tt>delete_all</tt> will either
          # do the deletion according to the strategy specified by the <tt>:dependent</tt> option, or
          # if no <tt>:dependent</tt> option is given, then it will follow the default strategy.
          # The default strategy is <tt>:nullify</tt> (set the foreign keys to <tt>nil</tt>), except for
          # +has_many+ <tt>:through</tt>, where the default strategy is <tt>delete_all</tt> (delete
          # the join records, without running their callbacks).
          #
          # There is also a <tt>clear</tt> method which is the same as <tt>delete_all</tt>, except that
          # it returns the association rather than the records which have been deleted.
          #
          # === What gets deleted?
          #
          # There is a potential pitfall here: +has_and_belongs_to_many+ and +has_many+ <tt>:through</tt>
          # associations have records in join tables, as well as the associated records. So when we

(in the rdoc for associations), it states: “The default strategy is :nullify (set the foreign keys to nil), except for has_many :through, where the default strategy is delete_all (delete the join records, without running their callbacks).”

I think that last statement is a little unclear since it is no longer accurate in Rails 4, it seems. Magne on S.O. also noted this in the first comment of this answer: What are the default values for Rails 3 for :dependent on has_many and belongs_to - Stack Overflow

In addition, that might be helpful to mention somewhere in guides/source/upgrading_ruby_on_rails.md?

I’m not sure how to summarize/clarify that behavior at the moment in associations.rb (would just removing the sentence about the default strategy be ok?) or in which places “dependent: :nullify” should be added to models to ensure similar behavior from Rails 3 to 4 for the upgrade doc. Any ideas?

Michael_Vogel · January 12, 2014, 7:54pm

Hi,

I’m new here, but I believe you should open an issue over at github. Then people could reference it for possible pull requests + it would be more visible if somebody searches for it.

Just my 2 cents.

Cheers